Variable stroke drives are used on a wide variety of machinery. A variable stroke drive may be used as a primary or secondary drive apparatus on various applications, for example, in the agricultural, metalworking, packaging, paper converting, sewing, and material handling industries.
In the textile industry, loom manufacturers use variable stroke drives as let-off mechanisms. The variable stroke drive controls the speed at which warp yarns are released. Further, the variable stroke drive maintains constant tension on the yams and, in effect, eliminates the need for a separate motor on the loom. Another example of an application for the variable stroke drive is in the food processing industry. A variable stroke drive may be used on a food press machine. The variable stroke drive controls the speed of a conveyor that proportions, forms, and stacks food products on a conveyor assembly. A further example of an application for a variable stroke drive is in the printing industry. Variable stroke drives may be used to control a high speed sheeter that controls the speed of stacking finished sheets after printing, and a separate variable stroke drive controls the cut-to-length of the paper sheets. Another example of an application for a variable stroke drive is on a grain dryer. The variable stroke drive controls the auger speed that circulates grain for proper, uniform drying.
There are numerous patents that disclose the concept of a variable speed power transmission apparatus. Two examples of variable stroke drives are shown in U.S. Pat. No. 2,950,623 (the '623 patent), issued to J. A. Weber, et al., and U.S. Pat. No. 3,340,743 (the '743 patent) issued to S. O. Stageberg.
The '623 patent discloses a drive mechanism having an input shaft that carries a crank arm. A first end of a chain is attached to the crank arm. Additionally, a first end of a spring is attached to the crank arm. The chain passes around a gear that is attached to an output shaft through a one-way clutch that includes a ratchet wheel and a pawl. The second end of the chain is attached to a second end of a spring. The spring wraps around a groove of a pulley member. The driving of the input shaft is intermittent and the amount of rotating may be controlled by the position of attachment on the crank arm to make longer or shorter the effective length of the crank arm in its operation of the driving mechanism of the invention. This invention discloses a variable eccentric that does not allow for greater output speed and output torque capabilities. Further, the patent discloses a constant driving mechanism with no new speed capacity. In addition, the '623 system is not capable of being adjusted while the input shaft is rotating, and it is an incremental indexing drive system and not a variable speed drive. Moreover, the '623 system does not provide a greater ratio of input to output speed to the extent that an overdrive is obtained.
The '743 patent discloses a variable speed power transmission. In this device, there are several belts or links. A single eccentric is mounted on an input shaft. The output shaft is connected to an overriding clutch. The device includes an arm that is usable to vary the amount of contact between the eccentric and belt or belts. A single eccentric comes into integral contact with a belt that urges a clutch disk to a first position to move an output shaft. A spring is connected directly to a clutch disk to return the clutch disk to an original position. The spring assembly is directly connected to the clutch disk. This arrangement creates a diminished angle of travel for the clutch disk, and in accord, this produces a lesser output shaft rotation. The '743 patent discloses a single eccentric with a 90.degree. phase angle differential between eccentrics. The single eccentric utilized transmits a relatively low speed to the output shaft. Further, the system of the '743 patent does not utilize a free-floating spring assembly in order to provide greater speed range for industrial applications. Moreover, the '743 system does not provide a greater ratio of input to output speed to the extent that an overdrive is obtained.
Therefore, a need exists for an improved apparatus that is capable of having a greater input to output ratio of rotation. A need exists for an improved apparatus that offers the capability of obtaining zero speed while the apparatus is operational. A related need is an apparatus that can be adjusted while the apparatus is operational or idle. A related need exists for a fixed length eccentric that utilizes a dual-eccentric transmission unit. Further, there is a need for a dual-eccentric transmission unit that has a 45.degree. phase angle differential between eccentric units. Last, there is a need for a free-floating spring assembly in order to provide greater speed ratio for industrial applications.